The test and simulation tableau integrated in the shaft alternator panel permits simulation of virtually all system functions without the main engine running. This permits operability to be tested even when docked.
Operating statuses and error messages can be seen on the tableau during starting and shut-down and during normal operation of the system. The following facilities are provided for this:
ü Alphanumeric display (LCD) for clear-text display in many national languages.
ü Storage of the errors or faults occurring consecutively in the event of a malfunction in a register so as to permit the original error or fault causing the malfunction to be recognized.
ü Colored LEDs for indicating errors, faults and operating statuses "at a glance".
ü Measuring instruments for indicating all important operating parameters with selection and indication of various computer software signals.
Improved availability thanks to fully digitalized control and monitoring system
The shaft alternator systems are equipped with a central, microprocessor-based computer for fully digitalized closed-loop control and open-loop control and for test and simulation. As compared with previous versions, this has dispensed with a large number of PC boards with relays for logic operations and with elements for analog and digital functions. This drastic reduction in the number of components results in a substantial improvement in reliability and availability.
Low overall volume thanks to diode rectifier
Only shaft alternator systems are designed with uncontrolled rectifiers between shaft alternator and inverter. This means that no control or tiring circuitry is required for the rectifier, thus greatly reducing the complexity of the electronics. The losses of diodes are less than those of thyristor rectifiers which are used on similar systems. The rectifier is mounted on top of the shaft alternator in space saving manner, thus providing a compact shaft alternator panel.
Less harmonics thanks to harmonic waves filter circuit, duplex choke or 12-pulse connection
The harmonic content at the output of the shaft alternator system has to be effectly reduced to admissible levels according to the classification rules to keep a mains voltage distortion factor of less than 8 %.
Therefore the shaft alternator system is configured depending on the load and on the system data with:
ü harmonic waves filter circuit,
ü duplex choke of
ü 12-pulse connection with mains transformer.
Trouble-free operation thanks to interference suppression filters
Trouble-free operation of even sensitive consumers is guaranteed by the high-frequency interference suppression filters.
Closed-loop control
Closed-loop control of the shaft alternator system maintains the mains voltage and the mains frequency constant. The automatic voltage regulator is incorporated in the compensator and operates in the same way as at a normal mains alternator.
The frequency controller acts on excitation of the shaft alternator. If the mains frequency is too low, as the result of a load increase or engine-speed reduction, the excitation of the shaft alternator is increased and it supplies a higher active current at constant voltage. The higher active power fed into the mains as the result of this causes a rise in frequency until a state of balance is reached between power fed in and power consumed, dependent upon the set frequency set value. In the reverse case, excitation of the shaft alternator is reduced if the mains frequency is too high so that the shaft alternator supplies a lower active current at constant voltage and so that the mains frequency drops accordingly.
The frequency set value can be set manually as on a diesel generator set or by the superordinated active-power load controller of an automatic power supply system. The active power between diesel generator sets operating in parallel can then be distributed in such a way that the shaft alternator, as the most economical source of energy, is fully loaded first and only the power required over and above this is supplied by the auxiliary diesel generator sets. In this case, the actual load does not drop below the minimum load required for the auxiliary diesel engines.
Shaft alternators on board ships are alternators driven by the main engine to supply power to the mains. The mains must be supplied with constant voltage and frequency by the shaft alternator even at changing speeds of the main engine, i.e. when the vessel travels at different speed ranges or if the propeller speed fluctuates very greatly in heavy seas.
On ships with fixed pitched propellers, the speed is set via the propeller speed. If using controllable pitch propellers, the shaft speed and the propeller pitch are adjusted simultaneously in order to achieve optimum propeller efficiency in this so-called combiner mode. Even with this type of propeller, it is thus economical to use shaft alternator systems with frequency converter for variable speed in order to permit combiner mode.
STN Systemtechnik Nord, partly a successor of AEG Marine Division, has been delivering shaft alternator systems with frequency converter since 1967. Over 200 ships have been equipped with them to date. Renowned shipyards and shipping companies have used our systems repeatedly.
The basic concept has remained unchanged since it has proven its advantages very well. System components have been improved constantly so that our shaft alternator systems are always state-of-the-art.
